Not applicable.
1. Field of the Invention
This invention relates to molded plastic containers which are made to be stacked one on top of another.
2. Discussion of Prior Art
Bulk boxes or containers for shipment and storage may, when filled, weigh many hundreds, or even a few thousand, pounds. To conserve space in transit and storage, it is desirable that these containers be stacked one on top of another. Therefore, the load supported on the bottom container may be many thousands of pounds.
These containers are often molded of plastic materials and are made to be reusable. They must, therefore, be capable of supporting the weight without permanent deformation. It is also desirable that such boxes be nestable, so that when they are emptied they may be nested inside one another and returned for refilling.
The invention provides a bulk container, including a lid, which is capable of bearing high stacking loads when one container is stacked on top of the lid of the next lower container.
Specifically, the present invention provides a plastic container for carrying heavy loads having a receptacle and a lid. The receptacle is formed of upright walls joined together at a lower edge by a bottom so as to define an open cavity closable by the lid. The lid has a support surface on which the bottom of a second container stacked thereon is supported. An elongated reinforcing member is secured to the lid beneath the bottom of the second container so as to support the second container. The reinforcing member substantially spans the upright walls on opposite sides of the receptacle and is supported above the upright walls by a saddle which cradles the reinforcing member and distributes loading from the reinforcing member to the lid.
In a preferred embodiment, the receptacle bottom has three flat feet that project downwardly and the support surface of the lid defines three recessed surfaces sized to receive the feet of a second receptacle stacked thereon. The feet are spaced apart in parallel to define a pair of channels sized to receive forks from a forklift. Three reinforcing members are disposed in grooves extending substantially along the middle of the recessed surfaces so as to underlie said feet of receptacle stacked thereon. The saddles are recessed in portions of the lid. Each saddle has a generally U-shaped center portion, and wings extending laterally outwardly from upper ends of the center portion. Lower surfaces of the center portion and wings bear against surfaces of the lid.
One feature of the container that contributes to its high stacking-strength is that it includes the rigid reinforcing members disposed in the lid. Forces are transferred from the lid at the ends of the reinforcing members to the container walls below. The members extend long enough all the way across the width of the container so as to overlap the lower container""s side walls at the ends of the members. Forces are transferred from the ends of the members to the lid by the saddles which extends below each member up along the sides of the member and out laterally from the sides of the member.
Another feature of the invention which contributes to the high stacking strength of the container is that the upper portion of the container is abruptly enlarged in relation to the lower portion. The abrupt enlargement creates a horizontal convolution which encircles the container for 360xc2x0 and contributes to the ability of the sides of the container to resist bulging. It does this while permitting the use of generally vertically running convolutions in the side walls of the container, both in the lower portion and in the upper portion. However, the vertical convolutions in the upper portion are preferably offset from the convolutions in the lower portion to provide horizontal surfaces or cross sections that resist bulging and buckling of the side walls of the container.
Still another strength enhancing feature is that the corners of the container, where the top portion transitions to the smaller portion, are more gradually transitioned to the smaller portion than the sides of the container. This may be done with a sloping surface, or a generally conical section of a surface to join the enlarged top portion of the container to the relatively smaller bottom portion of the container at the corners of the container. Thus, the ability of the corners to withstand vertical loading is significantly increased to resist collapse of the corners.
These and other advantages of the invention will be apparent from the detailed description and drawings.